Methods of electroless deposition of nickel, and methods of forming under bump metallurgy, and constructions comprising solder bumps

ABSTRACT

The invention includes a method of electroless deposition of nickel over an aluminum-containing material. A mass is formed over the aluminum-containing material, with the mass predominantly comprising a metal other than aluminum. The mass is exposed to palladium, and subsequently nickel is electroless deposited over the mass. The invention also includes a method of electroless deposition of nickel over aluminum-containing materials and copper-containing materials. The aluminum-containing materials and copper-containing materials are both exposed to palladium-containing solutions prior to electroless deposition of nickel over the aluminum-containing materials and copper-containing materials. Additionally, the invention includes a method of forming a solder bump over an aluminum-containing material.

TECHNICAL FIELD

[0001] The invention pertains to methods of electroless deposition ofnickel over aluminum-containing materials and copper-containingmaterials, and in particular embodiments pertains to methods of formingunder bump metallurgy (UBM) for subsequent solder bumps.

BACKGROUND OF THE INVENTION

[0002] Conductive bumps are currently being utilized for connectingintegrated circuitry associated with a semiconductor chip to othercircuitry external of the integrated circuitry. Solder bumps areutilized in, for example, flip chip applications, multi-chip moduleapplications, and chip scale packaging applications.

[0003] An exemplary solder bump construction is described with referenceto FIG. 1. Specifically, FIG. 1 illustrates a fragment 10 of asemiconductor construction. Fragment 10 comprises a substrate 12 havinga conductive layer 14 supported thereon. Substrate 12 can include asemiconductive material, such as, for example, monocrystalline silicon.To aid in interpretation of the claims that follow, the terms“semiconductive substrate” and “semiconductor substrate” are defined tomean any construction comprising semiconductive material, including, butnot limited to, bulk semiconductive materials such as a semiconductivewafer (either alone or in assemblies comprising other materialsthereon), and semiconductive material layers (either alone or inassemblies comprising other materials). The term “substrate” refers toany supporting structure, including, but not limited to, thesemiconductive substrates described above. Additionally, the terms“material” and “layer” are to be understood to encompass pluralities ofmaterials and layers, as well as single materials and layers, unlessspecifically stated otherwise.

[0004] Conductive material 14 can comprise a metallic material, such as,for example, one or more of aluminum and copper. In particularapplications, conductive material 14 comprises aluminum or copper.

[0005] Substrate 12 can further include various circuit components (notshown), such as, for example, capacitors and transistors; andadditionally can include insulative materials. Conductive material 14can electrically connect with various of the circuit componentsassociated with substrate 12.

[0006] An adhesion layer 16 is formed over conductive material 14.Adhesion layer 16 comprises, for example, titanium; and is utilized toimprove adhesion of a masking material to the conductive material 14.For instance, if conductive material 14 comprises aluminum, atitanium-containing adhesion layer 16 can improve adhesion of variousmasking materials (such as materials comprising polyamide or BCB) overthe aluminum.

[0007] A masking layer 18 is formed over adhesion layer 16. Maskinglayer 18 can comprise, for example, polyamide or BCB materials (with BCBmaterials being materials derived from bisbenzocyclobutane chemistry).Masking layer 18 can be patterned by providing photoresist (not shown)over the masking layer, using photolithographic methods to pattern thephotoresist, and subsequently transferring a pattern from thephotoresist to layer 18 with an appropriate etch.

[0008] The patterning of masking layer 18 forms an opening 20 extendingthrough patterned masking layer 18. Opening 20 is shown extendingthrough adhesion layer 16 and to conductive material 14. The shownopening 20 can be formed by first patterning masking layer 18 to exposea portion of adhesion layer 16, and subsequently removing the exposedportion of adhesion layer 16 to extend the opening entirely throughlayer 16 and to conductive material 14.

[0009] A nickel-containing layer 22 is formed within opening 20 and overconductive material 14. Nickel-containing layer 22 can be formed by, forexample, electroless deposition, which is also referred to asautocatalytic electrolytic deposition (AED). Prior to the electrolessdeposition of nickel-containing layer 22, aluminum-containing material14 within opening 20 is cleaned, and then subjected to activation with azinc-containing solution. Such activation forms a thin zinc-containingmaterial (not shown) over aluminum-containing layer 14. Subsequently,nickel-containing layer 22 is formed on the thin zinc-containingmaterial by reduction of nickel from a nickel salt. An exemplarychemistry for electroless deposition of zinc comprises reactions I andII.

[0010] I. NiSO₄+2e−→Ni+SO₄ ²⁻

[0011] II. 3H⁺+(NH₄)₂H₃P₂O₄→2NH₄ ⁺+2H₃PO₂ ⁻+2e−

[0012] After formation of nickel-containing layer 22, a gold-containinglayer 24 is formed over nickel-containing layer 22. Gold-containinglayer 24 can be formed by electroless deposition utilizing, for example,gold sulfide as a source of gold. The gold can be used as a wettingagent for subsequent solder formation.

[0013] It is noted that nickel-containing layer 22 can consist of, orconsist essentially of, nickel; and that gold-containing layer 24 canconsist of, or consist essentially of, gold.

[0014] A solder bump 26 is formed over gold-containing layer 24. Solderbump 26 can comprise, for example, a tin and/or lead-based solder.

[0015] The methodology described above is typical of what would beutilized for forming a solder bump over a layer 14 which comprisespredominantly aluminum (i.e, comprises more than 50 atomic percentaluminum), consists essentially of aluminum, or consists of aluminum. Iflayer 14 comprises copper, the methodology will typically be somewhatdifferent. For instance, adhesion layer 16 will typically be eliminated,and masking layer 18 will typically comprise butylcyclobutene (BCB).Further, a layer 14 which comprises predominantly copper, consistsessentially of copper, or consists of copper, will typically be exposedto an activation solution which comprises palladium, instead of zinc, toform a thin layer of palladium (not shown) over layer 14. Subsequently,nickel-containing layer 22 will be formed over the thin layer ofpalladium utilizing the electroless chemistry described previously, andgold layer 24 will be formed over nickel-containing layer 22 utilizingelectroless chemistry. Finally, solder bump 26 can be formed over goldlayer 24.

[0016] It would be desirable to develop improved methods for formingelectrical connections from solder bumps to conductive materialsassociated with semiconductor substrates.

SUMMARY OF THE INVENTION

[0017] In one aspect, the invention encompasses a method of electrolessdeposition of nickel over an aluminum-containing material. A mass isformed over the aluminum-containing material, with the masspredominantly comprising a metal other than aluminum. The mass isexposed to palladium, and subsequently nickel is electroless depositedover the mass.

[0018] In another aspect, the invention encompasses a method ofelectroless deposition of nickel over aluminum-containing materials andcopper-containing materials. The aluminum-containing materials andcopper-containing materials are both exposed to palladium-containingsolutions prior to electroless deposition of nickel over thealuminum-containing materials and copper-containing materials.

[0019] In another aspect, the invention encompasses a method of forminga solder bump over a first material. The first material comprises one orboth of aluminum and copper material. A titanium-containing material isformed over the first material, and a patterned mask is formed over thetitanium-containing material. The patterned mask comprises polyamideand/or a BCB material, and has an opening extending therethrough to thetitanium-containing material to expose a portion of thetitanium-containing material. A palladium-containing material is formedon the exposed portion of the titanium-containing material. Anickel-containing material is electroless deposited on thepalladium-containing material, and a gold-containing material is formedon the nickel-containing material. Finally, a solder bump is formed overthe gold-containing material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0021]FIG. 1 is a diagrammatic, cross-sectional view of a semiconductorwafer fragment formed in accordance with the prior art.

[0022]FIG. 2 is a diagrammatic, cross-sectional view of a semiconductorwafer fragment at a preliminary process step in accordance with a methodof the present invention.

[0023]FIG. 3 is a view of the FIG. 2 wafer fragment shown at a processstep subsequent to that of FIG. 2.

[0024]FIG. 4 is a diagrammatic, cross-sectional view of a semiconductorwafer fragment formed in accordance with another embodiment method ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] A method encompassed by the present invention is describedinitially with reference to FIGS. 2 and 3. In describing FIGS. 2 and 3,similar numbering will be utilized as was used above in describing theprior art of FIG. 1.

[0026] Referring to FIG. 2, a fragment 50 of a semiconductor wafer isillustrated. Fragment 50 comprises a substrate 12 having a conductivematerial 14 thereover. Conductive material 14 can comprise a metal, suchas, for example, copper or aluminum. In the shown embodiment, material14 is preferably an aluminum-containing material, such as, for example,a material which comprises predominantly aluminum, consists essentiallyof aluminum, or consists of aluminum.

[0027] A mass 16 is formed over aluminum-containing material 14. Mass 16predominantly comprises a metal other than aluminum, and in particularembodiments can be a titanium-containing material. Suchtitanium-containing material can predominantly comprise titanium,consist essentially of titanium, or consist of titanium.

[0028] A masking layer 18 is formed over mass 16. Masking layer 18 cancomprise, for example, polyamide or BCB, and can be patterned utilizingconventional methods. For instance, a patterned photoresist (not shown)can be formed over material 18, and subsequently a pattern transferredfrom the photoresist to material 18 with a suitable etch.

[0029] A thin palladium-containing layer 52 is formed overtitanium-containing layer 16. Palladium-containing layer 52 cancomprise, consist essentially of, or consist of palladium.Palladium-containing layer 52 will typically be an adsorbed monolayer.

[0030] It is noted that masking material 18 covers a portion 54 oftitanium-containing layer 16, while leaving another portion 56 oftitanium-containing layer 16 exposed. Palladium-containing layer 52 isformed over the exposed portion 56 of titanium-containing layer 16, andis not formed over the portions 54 which are covered by masking layer18. It is further noted that some of the palladium of layer 52 canextend into layer 16, so that an interface between layers 52 and 16 willbe more diffuse than is illustrated.

[0031] Palladium-containing layer 56 can be formed by exposingtitanium-containing mass 16 to a solution comprising palladium and ahalogen acid. An exemplary solution comprises from about 0.1 grams/literto about 0.4 grams/liter PdCl₂ and from about 4 milliliters/liter toabout 25 milliliter/liter of 49% HF, with the remaining portion of thesolution being water. HCl can be utilized in addition to, oralternatively to, the HF. The exposure of mass 16 to thepalladium-comprising solution is preferably for a time of from about 5seconds to about 60 seconds, and at a temperature of about roomtemperature (i.e., from about 10° C. to about 30° C.).

[0032] Construction 50, like the prior art construction 10 of FIG. 1,comprises a masking layer 18 having an opening 20 extendingtherethrough. However, unlike the prior art construction 10 of FIG. 1,titanium-containing layer 16 remains within the opening 20 duringformation of an activation layer (layer 52) over titanium-containingmaterial 16. Further, a palladium-containing solution is utilized toform the activating layer over an aluminum-containing layer 14, incontrast to the prior art construction of FIG. 1 in which a zincsolution would be utilized for forming the activating layer relative toan aluminum-containing layer 14.

[0033] Referring to FIG. 3, a nickel-containing layer 22 is electrolessdeposited over palladium-containing layer 15, and a gold layer 24 isformed over nickel-containing layer 22. In the shown embodiment,palladium-containing layer 52 is physically against titanium-containinglayer 16, nickel-containing layer 22 is physically againstpalladium-containing layer 52, and gold-containing layer 24 isphysically against nickel-containing layer 22.

[0034] A solder bump 26 is formed over gold-containing layer 24.

[0035] An advantage of the processing of the present invention relativeto prior art processes for electroless deposition of nickel overaluminum-containing materials is that the process of the presentinvention can utilize a palladium-containing solution for activationover an aluminum-containing layer. Specifically, the prior art describedwith reference to FIG. 1 would utilize a zinc-containing solution todirectly activate a surface of an aluminum-containing layer 14. Incontrast, preferred methodology of the present invention provides atitanium-containing layer 16 over aluminum-containing layer 14, andsubsequently utilizes a palladium-containing solution to activate thetitanium-containing layer 16.

[0036] An advantage of utilizing a palladium-containing solution toactivate relative to an aluminum-containing layer is that such enablesthe same palladium-containing solution to be utilized for activatingrelative to both aluminum-containing layers and copper-containinglayers. Specifically, it was discussed relative to FIG. 1 thatpalladium-containing solutions can be utilized to directly activatecopper-containing layers prior to electroless deposition of nickel overthe copper-containing layers. Such is further illustrated with referenceto FIG. 4 wherein a semiconductor construction 100 is illustrated. Inreferring to construction 100, similar numbering would be used as wasutilized above in describing FIG. 1.

[0037] Construction 100 comprises a substrate 12, a copper-containingconductive layer 14, and a patterned masking layer 18. Patterned maskinglayer 18 can comprise, for example, butylcyclobutene. An opening 20extends through masking layer 18 to a portion 104 of copper-containingmaterial 14. A palladium-containing layer 102 is formed over exposedportion 104. Palladium-containing layer 102 can be considered anactivating layer, and is formed by exposing fragment 100 to apalladium-containing solution. A nickel-containing layer 22 iselectroless deposited over activating layer 104, a gold-containing layer24 is formed over nickel-containing layer 22, and a solder bump 26 isformed over gold-containing layer 24.

[0038] In preferred embodiments, the palladium-containing solutionutilized for forming palladium-containing layer 102 of FIG. 4 will beidentical to the solution described above with reference to FIGS. 2 and3 for forming palladium-containing layer 52. Accordingly, the samesolution can be utilized for activating relative to copper-containingmaterials as was utilized for activating relative to aluminum-containingmaterials.

[0039] An advantage of utilizing the same solution for activatingrelative to aluminum-containing layers and copper-containing layers isthat such can reduce the number of processing solutions maintained at asemiconductor fabrication facility, and can save on tooling at thefacilities, while maintaining throughput. Currently, semiconductorfabrication frequently involves electroless nickel deposition over bothaluminum-containing wiring layers and copper-containing wiring layers.The prior art methodology of FIG. 1 utilizes a different activationsolution for activating relative to the copper-containing layers than isutilized for activating relative to the aluminum-containing layers.Methodology of the present invention can enable a single solution to bemaintained at a semiconductor production facility, and such solution canbe utilized for activating relative to both aluminum-containingmaterials and copper-containing materials. In particular aspects of theinvention, a palladium-containing solution is in a tank, and thecopper-containing substrates and aluminum-containing substrates aretreated by dipping the substrates into the tank. Titanium-containinglayers can be formed over aluminum-containing materials of thealuminum-containing substrates prior to dipping the aluminum-containingsubstrates in the tank; and titanium-containing layers can also beformed over copper-containing materials of the copper-containingsubstrates prior to dipping the copper-containing substrates in thetank.

[0040] In other embodiments of the present invention, a separatesolution can be utilized for activating relative to copper-containingmaterials than is used for activating relative to aluminum-containing,but both solutions can comprise palladium and a halogen acid.Accordingly, the solutions will comprise a similar or identical chemicalconstituents as one another, which can reduce a number of chemicalconstituents that are stocked at a semiconductor production facility. Adifference between the solution utilized for activation relative tocopper-containing layers and that utilized for activation relative toaluminum-containing layers can be in the concentration of palladium inone solution relative to the other, or in the concentration and/or typeof halogen acid utilized in one solution relative to the other.

[0041] In embodiments in which a single common solution is utilized toactivate relative to both aluminum-containing layers andcopper-containing layers, methodology can be altered to accommodatedifferent reaction rates relative to the copper-containing layers andthe titanium-containing layers associated with aluminum-containinglayers. Specifically, if the titanium-containing layers react moreslowly with a particular palladium-containing activating solution thando copper-containing layers, the titanium-containing layers can beexposed to the solution for a longer period of time than are thecopper-containing layers. Alternatively, if it is found that thecopper-containing layers react more slowly than the titanium-containinglayers, the copper-containing layers can be exposed to thepalladium-containing activating solution for a longer period of timethan are the titanium-containing layers.

[0042] A further aspect of the present invention is that a titanium masscan be provided over a copper-containing layer prior to exposure to anactivating palladium solution. In such aspect of the invention, themethodology of FIGS. 2 and 3 can be applied to a construction in whichlayer 14 predominantly comprises copper, consists essentially of copper,or consists of copper. This aspect of the invention can be particularlyadvantageous in applications in which a single common palladium solutionis utilized for activating relative to both aluminum-containing layersand copper-containing layers in that it can alleviatecross-contamination when switching from aluminum-containing layers tocopper-containing layers and vice versa. Specifically, a materialexposed to the palladium-containing activation solution will be atitanium-containing layer (16 of FIGS. 2 and 3), regardless of whetherthe activation is relative to a conductive material (14 of FIGS. 2 and3) which is predominantly copper or aluminum. Also, the covering of bothaluminum-containing conductive materials and copper-containing materialswith a same composition of titanium prior to exposure to the palladiumsolution can enable identical palladium activation to be obtainedrelative to the copper-containing materials and aluminum-containingmaterials.

[0043] Another advantage of particular aspects of the present inventionis that a number of processing steps can be reduced relative to priorart methods. Specifically, particular aspects of the present inventioncan eliminate formation of an opening (20 in FIG. 1) entirely through atitanium-containing layer (16 in FIG. 1).

[0044] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of electroless deposition of nickel over a materialcomprising one or both of copper and aluminum, comprising: forming amass over the material, the mass predominantly comprising a metal otherthan aluminum or copper; exposing the mass to palladium; and afterexposing the mass to palladium, electroless depositing nickel over themass.
 2. The method of claim 1 wherein the material predominantlycomprises aluminum.
 3. The method of claim 1 wherein the materialconsists essentially of aluminum.
 4. The method of claim 1 wherein thematerial consists of aluminum.
 5. The method of claim 1 wherein thematerial predominantly comprises copper.
 6. The method of claim 1wherein the material consists essentially of copper.
 7. The method ofclaim 1 wherein the material consists of copper.
 8. The method of claim1 wherein the exposing the mass to palladium comprises exposing the massto a solution comprising palladium and a halogen acid.
 9. The method ofclaim 1 wherein the mass predominantly comprises titanium.
 10. Themethod of claim 1 wherein the mass predominantly comprises titanium andthe material predominantly comprises aluminum.
 11. The method of claim 1wherein the mass predominantly comprises titanium and the materialpredominantly comprises copper.
 12. The method of claim 1 wherein themass predominantly comprises titanium, and further comprising: beforeexposing the mass to palladium, forming a masking layer over the mass;and patterning the masking layer to leave a portion of the mass coveredby the masking layer and another portion of the mass not covered by themasking layer, the exposing to the palladium comprising exposing onlythe portion of the mass which is not covered by the masking layer. 13.The method of claim 12 wherein the masking layer comprises polyamide.14. The method of claim 12 wherein the masking layer comprises a BCBmaterial.
 15. The method of claim 1 wherein the exposing the mass topalladium comprises exposing the mass to a solution comprising palladiumand a halogen acid for a time of from about 5 seconds to about 60seconds.
 16. The method of claim 1 wherein the exposing the mass topalladium comprises exposing the mass to a solution comprising palladiumand a halogen acid for a time of from about 5 seconds to about 60seconds, and at a temperature of from about 10° C. to about 30° C. 17.The method of claim 1 wherein the exposing the mass to palladiumcomprises exposing the mass to a solution comprising palladium and oneor both of HF and HCl.
 18. The method of claim 1 wherein the exposingthe mass to palladium comprises exposing the mass to a solutioncomprising from about 0.1 grams/liter to about 0.4 grams/liter PdCl₂,and from about 4 milliliters/liter to about 25 milliliters/liter of 49%HF.
 19. A method of electroless deposition of nickel over a firstmaterial, comprising: forming a titanium-containing material over thefirst material; forming a palladium-containing material over thetitanium-containing material; and electroless depositing nickel on thepalladium-containing material.
 20. The method of claim 19 wherein thefirst material predominantly comprises aluminum.
 21. The method of claim19 wherein the first material predominantly comprises copper.
 22. Themethod of claim 19 wherein the forming the palladium-containing materialcomprises exposing the titanium-containing material to a solutioncomprising palladium and a halogen acid.
 23. The method of claim 19wherein the forming the palladium-containing material comprises exposingthe titanium-containing material to a solution comprising palladium anda halogen acid for a time of from about 5 seconds to about 60 seconds.24. The method of claim 19 wherein the forming the palladium-containingmaterial comprises exposing the titanium-containing material to asolution comprising palladium and a halogen acid for a time of fromabout 5 seconds to about 60 seconds, and at a temperature of from about10° C. to about 30° C.
 25. The method of claim 19 wherein the formingthe palladium-containing material comprises exposing thetitanium-containing material to a solution comprising palladium and oneor both of HF and HCl.
 26. The method of claim 19 wherein the formingthe palladium-containing material comprises exposing thetitanium-containing material to a solution comprising from about 0.1grams/liter to about 0.4 grams/liter PdCl₂, and from about 4milliliters/liter to about 25 milliliters/liter of 49% HF.
 27. A methodof electroless deposition of nickel over aluminum-containing materialsand copper-containing materials, comprising: providing a first substrateand a second substrate in a common semiconductor fabrication facility;the first substrate having a copper-containing material, and the secondsubstrate having an aluminum-containing material; forming atitanium-containing material over the aluminum-containing material ofthe second substrate; exposing the first substrate to a firstpalladium-containing solution to form a first palladium-containing layerover the copper-containing material; exposing the second substrate to asecond palladium-containing solution to form a secondpalladium-containing layer over the titanium-containing material;electroless depositing nickel on the first palladium-containing materialto form a first nickel-containing material on the firstpalladium-containing material; and electroless depositing nickel on thesecond palladium-containing material to form a second nickel-containingmaterial on the second palladium-containing material.
 28. The method ofclaim 27 wherein the copper-containing material of the first substrateis contacted with the first palladium-containing solution to form thefirst palladium-containing layer over the copper-containing material.29. The method of claim 27 further comprising forming atitanium-containing material over the copper-containing material of thefirst substrate and exposing the titanium-containing material over thefirst substrate to the first palladium-containing solution to form thefirst palladium-containing layer over the copper-containing material.30. The method of claim 27 wherein the first and secondpalladium-containing solutions are a single common solution.
 31. Themethod of claim 27 wherein the first and second palladium-containingsolutions are a single common solution in a tank, and wherein theexposing of the first and second substrates comprises dipping the firstand second substrates into the tank.
 32. The method of claim 27 whereinthe first and second palladium-containing solutions are a single commonsolution which comprises palladium and a halogen acid.
 33. The method ofclaim 27 wherein the first and second palladium-containing solutions area single common solution which comprises palladium and one or both of HFand HCl.
 34. The method of claim 27 wherein the first and secondpalladium-containing solutions are a single common solution whichcomprises from about 0.1 grams/liter to about 0.4 grams/liter PdCl₂, andfrom about 4 milliliters/liter to about 25 milliliters/liter of 49% HF.35. The method of claim 27 wherein the first and secondpalladium-containing solutions are a single common solution, and whereinthe first substrate is exposed to the common solution for a differentlength of time than the second substrate is exposed to the commonsolution.
 36. The method of claim 27 wherein the first and secondpalladium-containing solutions are different solutions from one another.37. The method of claim 27 wherein the first and secondpalladium-containing solutions are different solutions from one another,and comprise different concentrations of palladium relative to oneanother.
 38. The method of claim 27 further comprising: forming a firstgold-containing material over the first nickel-containing material;forming a second gold-containing material over the secondnickel-containing material; forming a first solder bump over the firstgold-containing material; and forming a second solder bump over thesecond gold-containing material.
 39. A method of forming a solder bumpover an aluminum-containing material, comprising: forming atitanium-containing material over the aluminum-containing material;forming a patterned mask over the titanium-containing material; thepatterned mask comprising polyamide or a BCB material, and having anopening extending therethrough to the titanium-containing material toexpose a portion of the titanium-containing material; forming apalladium-containing material on the exposed portion of thetitanium-containing material; electroless depositing a nickel-containingmaterial on the palladium-containing material; forming a gold-containingmaterial on the nickel-containing material; and forming a solder bumpover the gold-containing material.
 40. The method of claim 39 whereinthe forming the palladium-containing material comprises contacting theexposed portion of the titanium-containing material with a solutioncomprising palladium and a halogen acid.
 41. The method of claim 39wherein the forming the palladium-containing material comprisescontacting the exposed portion of the titanium-containing material witha solution comprising palladium and a halogen acid for a time of fromabout 5 seconds to about 60 seconds.
 42. The method of claim 39 whereinthe forming the palladium-containing material comprises contacting theexposed portion of the titanium-containing material with a solutioncomprising palladium and a halogen acid for a time of from about 5seconds to about 60 seconds, and at a temperature of from about 10° C.to about 30° C.
 43. The method of claim 39 wherein the forming thepalladium-containing material comprises contacting the exposed portionof the titanium-containing material with a solution comprising palladiumand one or both of HF and HCl.
 44. The method of claim 39 wherein theforming the palladium-containing material comprises contacting theexposed portion of the titanium-containing material with a solutioncomprising from about 0.1 grams/liter to about 0.4 grams/liter PdCl₂,and from about 4 milliliters/liter to about 25 milliliters/liter of 49%HF.